1. Field of Invention
This invention relates to the use of direct-current power sources with adjustable no-load voltages and adjustable internal impedances, specifically for use in special effects devices for musical instruments.
2. Description of Prior Art
Musicians, particularly guitarists, often employ the use of special effects devices in the signal line between their instruments and the amplifying equipment. These devices are used to produce audio effects such as signal distortion, regenerative time delays, and signal doubling (often referred to as chorusing).
Many of the special effects devices are designed to use either batteries or AC-to-DC power supplies as power sources.
However, there is reluctance by many musicians to use any power source other than batteries. This is because they prefer the way batteries alter the sound output from some special effects as they begin to run down. As the voltage supplied to these special effect devices decreases, the tonal quality of the device tends to change in a way that is desirable to the musicians, this change not being achievable from a traditional AC-to-DC power supply.
Such change in tone is further accentuated in certain special effects devices that draw sudden bursts of current from the battery when the input signal increases suddenly, since the internal impedance of a battery increases as it runs down, thereby further decreasing the voltage during a surge in current demand.
The desire to achieve this tonal quality is strong enough among many musicians such that they spend time and money buying fresh batteries, intentionally discharging them to certain levels, then labeling and storing the batteries until they are to be used in performances.
The main problem with this approach is that, aside from the cost in time and money for preparing the batteries, the batteries only operate in the desired state of discharge for a period of time before they become totally unusable. This useful time is sometimes shorter than the duration of the performance, resulting in the need to change batteries during a performance.
Some manufacturers of AC-to-DC power supplies have attempted to remedy this problem by offering supplies with output voltage adjustments built-in. While this solves the problem of providing a voltage that can be set to a level that produces the desired tonal quality under normal signal conditions, it does not address the problem of simulating the voltage fluctuations of a real battery under sudden current demand conditions.
Described by Esser et al. (U.S. Pat. No. 4,878,009) is a power supply arrangement that provides for adjusting both the no-load voltage output and the internal impedance. However, that patent specifies the design for use as a testing apparatus. It does not consider the design for use as a power source other than to allow characterization of the load under undesirable power supply conditions. It treats internal impedance as an undesirable attribute of a power source, not as a beneficial attribute as in the case of its use in musical instrument special effects devices.